Slammer could have been much worse

The Slammer worm took just 10 minutes to infect 90 per cent of vulnerable servers, making it the fastest spreading virus in history.

As it began scouring the internet, it doubled in size every 8.5 seconds, according to a report published by the Cooperative Association for Internet Data Analysis.

The report warned: "If the worm had carried a malicious payload, had attacked a more widespread vulnerability, or had targeted a more popular service, the effects would likely have been far more severe."

The worm infected at least 75,000 servers, and perhaps considerably more. The report said that Slammer achieved its full rate of over 55 million scans per second after just three minutes.

After this the rate of growth slowed down because large portions of the internet did not have enough bandwidth to allow it to operate unhindered.

The report described the attack as a "significant milestone in the evolution of computer worms", and warned that these sorts of bugs "should be considered a standard tool in the arsenal of an attacker".